Cliff:
I have no trouble distinguishing between cyanobacterias and filamentous hair algae, and this is most definitely not a cyano. I'm 99% certain it's a species of either derbesia or cladophoropsis. I'll be finding out for 100% certain next week.
I've never had cyano in this tank, but have fought with this hair algae for a couple of years. Very persistant, tough stuff, and I'm anxious to finally get a positive ID on it. AlgaeFix is supposed to be effective against cladophora, so I'm betting on derbesia, which is what I believed it was from the beginning.
I've always assumed that carbon, polyfilter, Seagel, etc. would, at least temporarily, significantly reduce the effectiveness of the AlgaeFix. The GAC and Polyfilter I'm now running was a month old when I started dosing the AlgaeFix, and by now it must surely be making only a minimal (if any at all) impact. I think I'll take a break from the AlgaeFix for a couple of weeks, do some regular water changes, and then try again without any kind of chemical filtration at all running and see what happens. Could be interesting...